It is important to form high density contact holes or via openings in a wafer for some devices. Due to lithography process limitations, however, it is sometimes difficult to create high density contact holes or via openings as desired. For example, in the case of forming contact holes in a dielectric layer, the size or diameter of the contact holes formed by lithography process are relatively large in diameter, such as more than half of the pitch size. This results in low density array of contact holes to be formed, which is not preferred for certain devices. Furthermore, forming small size contact holes is much more challenging than forming small size trenches because of diffraction in both X and Y directions.
From the foregoing discussion, it is desirable to provide high density array of contact holes with small size and dimension in a wafer. There is also a need to provide a simplified and cost efficient method to form these high density array of contact holes.